Laser Converging Apparatus, Optical Pickup Device and Optical Disc Recording/Reproduction Apparatus

ABSTRACT

A laser converging apparatus is disclosed that comprises a polarizing hologram element having a first area defined by a numerical aperture corresponding to a thickness of a first protective layer of a first disk medium and a second area inside the first area, the second area defined by a numerical aperture corresponding to a thickness of a second protective layer (&gt;the thickness of the first protective layer) of a second disk medium, the second area having a hologram pattern for transmitting first laser light linearly polarized in a first direction without diffracting the first laser light while diffracting and transmitting second laser light that is linearly polarized in a second direction crossing the first direction at right angles, the second laser light having the same wavelength as the first laser light; an objective lens having the numerical aperture corresponding to the thickness of the first protective layer, the objective lens converging the first laser light having passed through the first area including the second area onto an information surface on one side of the first protective layer, the objective lens converging the second laser light having passed through the second area onto an information surface on one side of the second protective layer; and a holder that holds the polarizing hologram element and the objective lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2005-194311, filed Jul. 1, 2005 in Japan, of which fullcontents are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser converging apparatus, anoptical pickup device, and an optical disk recording/reproducingapparatus.

2. Description of the Related Art

An optical pickup device has been in popular use, which device includesa semiconductor laser that emits laser light of different wavelengths(780 to 790 nm for CD; 650 to 660 nm for DVD) onto optical disk mediahaving different protective layer thicknesses, such as a CD (CompactDisc) with a protective layer of 1.2 mm thick and a DVD (DigitalVersatile Disc) with a protective layer of 0.6 mm thick, and anobjective lens usable for both optical disk media. This optical pickupdevice corrects a spherical aberration caused by the difference betweenthe protective layer thicknesses, utilizing the difference between thewavelengths, to enable recording and reproduction on each optical diskmedium.

These days, however, newly proposed optical disk media have emerged.These media have respective different protective layer thicknesses, suchas a Blu-ray Disc (registered trademark) with a protective layer of0.075 to 0.1 mm thick and an HD DVD (High Definition DVD) with aprotective layer of 0.6 mm thick, and are capable of recording operationat higher density than CDs or DVDS. For the Blu-ray Disc, such anoptical pickup device is used that it includes a semiconductor laserthat emits blue-violet laser light having a wavelength of 400 to 410 nmand an objective lens having a numerical aperture (hereinafter referredto as NA) of 0.85. For the HD DVD, such an optical pickup device is usedthat it includes a semiconductor laser that emits the blue-violet laserlight having the same wavelength as that for the Blu-ray Disc and anobjective lens having an NA of 0.65. Individual optical pickup devices,therefore, are employed for the Blu-ray Disc and HD DVD, respectively.

These conventional optical pickup devices are, for example, disclosed inJP-A No. 14-184026 and described on page 115 of DVD Textbook by HarukiTokumaru, Fumihiko Yokokawa, and Mitsuru Irie.

Recoding and reproducing on both Blu-ray Disc and HD DVD, however,requires individual pickup devices compatible respectively with theBlu-ray Disc and HD DVD. This raises a problem of higher cost, largersize, and heavier weight of pickup devices. The same problem happens inan optical disk recording/reproducing apparatus into which the opticalpickup devices are incorporated. Besides, applying the blue-violet laserlight of the same wavelengths to Blu-ray Disc and HD DVD makesimpossible the employment of the conventional method utilizing thedifferences between wavelengths, thus makes difficult manufacturing ofan optical pickup device that can be used for both Blu-ray Disc and HDDVD.

SUMMARY OF THE INVENTION

In order to solve the above problem, a major aspect of the presentinvention provides a laser converging apparatus comprising a polarizinghologram element having a first area defined by a numerical aperturecorresponding to a thickness of a first protective layer of a first diskmedium and a second area inside the first area, the second area definedby a numerical aperture corresponding to a thickness of a secondprotective layer (>the thickness of the first protective layer) of asecond disk medium, the second area having a hologram pattern fortransmitting first laser light linearly polarized in a first directionwithout diffracting the first laser light while diffracting andtransmitting second laser light that is linearly polarized in a seconddirection crossing the first direction at right angles, the second laserlight having the same wavelength as the first laser light; an objectivelens having the numerical aperture corresponding to the thickness of thefirst protective layer, the objective lens converging the first laserlight having passed through the first area including the second areaonto an information surface on one side of the first protective layer,the objective lens converging the second laser light having passedthrough the second area onto an information surface on one side of thesecond protective layer; and a holder that holds the polarizing hologramelement and the objective lens.

According to the present invention there can be provided a laserconverging apparatus, an optical pickup device, and an optical diskrecording/reproducing apparatus adaptable to optical disk media havingdifferent protective layer thicknesses using the same wavelength oflaser light.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding of the present invention and its advantages,the following description will be given for close reference, togetherwith the attached drawings.

FIG. 1 is a functional block diagram showing one example of the overallconfiguration of an optical pickup device according to the presentinvention;

FIG. 2 is a detail view of an objective lens and a polarizing hologramelement;

FIG. 3 is a front view of a hologram pattern formed on the polarizinghologram element;

FIG. 4 is a sectional view of the hologram pattern formed on thepolarizing hologram element;

FIG. 5 is a general block diagram for describing the operation of theoptical pickup device in application to an HD DVD medium;

FIG. 6 is a graphic diagram showing the exemplary state of Y directionlaser light in a laser converging apparatus and an HD DVD medium;

FIG. 7 is a graphic diagram showing a diffusion hologram pattern formedin the part of an NA 0.85 area other than an NA 0.65 area;

FIG. 8 is a graphic diagram showing another sectional shape of thehologram pattern;

FIG. 9 is a graphic diagram showing still another sectional shape of thehologram pattern;

FIG. 10 is a functional block diagram showing another example of theoverall configuration of the optical pickup device according to thepresent invention;

FIG. 11 is a detail view of the objective lens 10 and a nonpolarizinghologram element 24 shown in FIG. 10;

FIG. 12 is a general block diagram for describing the operation of theoptical pickup device in application to an HD DVD medium;

FIG. 13 is a detail view of the objective lens 10 and the nonpolarizinghologram element 24 shown in FIG. 10;

FIG. 14 is a graph depicting the intensity distribution of zero orderlight and permeated laser light;

FIG. 15 is a graphic diagram showing another form of the hologrampattern;

FIG. 16 is a functional block diagram showing another example of theoverall configuration of the optical pickup device according to thepresent invention;

FIG. 17 is a detail view of the objective lens, a nonpolarizing hologramelement, and a polarizing hologram element;

FIG. 18 is a detail view of a hologram pattern formed on thenonpolarizing hologram element;

FIG. 19 is a graphic diagram showing another form of the nonpolarilzinghologram pattern;

FIG. 20 is a functional block diagram showing still another example ofthe overall configuration of the optical pickup device according to thepresent invention; and

FIG. 21 is a detail view of the objective lens and the nonpolarizinghologram element.

DETAILED DESCRIPTION OF THE INVENTION

The description given by this specification and the drawings attachedthereto explain at least the following matters.

First Embodiment

=An Example of the Overall Configuration of an Optical Pickup Device toWhich a Laser Converging Apparatus Applies=

The following is a description of the overall configuration of the laserconverging apparatus (laser converging assembly) 19 and the opticalpickup device to which the laser converging apparatus 19 appliesaccording to the present invention. The description will be madereferring to FIGS. 1 to 4. FIG. 1 is a functional block diagram showingone example of the overall configuration of the optical pickup deviceaccording to the present invention. Left-oblique lines shown in FIG. 1represent a section of a lens holder 11, and represent the same also inother FIGS. than FIG. 1. FIG. 2 is a detail view of an objective lens 10and a polarizing hologram element 8 shown in FIG. 1. FIG. 3 is a planview of the hologram pattern formed on the polarizing hologram element8. FIG. 4 is a sectional view of Et hologram pattern formed on thepolarizing hologram element 8. In the following description, an opticaldisk medium conforming to the HD DVD standard is referred to as HD DVDmedium (second disk medium) 21, and an optical disk medium conforming tothe Blu-ray standard is referred to as Blu-ray medium (first diskmedium) 20. Also, an information recording layer in the optical diskmedium is referred to as information surface. In addition, the thicknessthat is equivalent to a distance incoming laser light from the opticalpickup device travels from one surface of the optical disk medium to theinformation surface is referred to as the thickness of a protectivelayer. The optical pickup device comprises a blue-violet semiconductorlaser 1 (semiconductor laser), a semiconductor laser (LD) drivingcircuit 2, a collimator lens 3, a liquid crystal element 4 (polarizationdirection switching element), a liquid crystal driving circuit 5, amirror 6, and the laser converging apparatus 19. The laser convergingapparatus 19 includes the polarizing hologram element 8, the objectivelens 10, and the lens holder 11. No drawings are given in FIG. 1,showing the optical pickup device, for an optical system, such as anoptical detector, for detecting FE (Focus Error) signals, TE (TrackingError) signals, RF (Radio Frequency) signals, etc., an opticalcomponent, and an actuator for driving the laser converging apparatus 19in a direction of focusing or tracking, which are incorporated into anordinary optical pickup device.

The blue-violet semiconductor laser 1 is, for example, composed ofdiodes consisting of p-type semiconductors and n-type semiconductorsjoined via pn junctions. When a control voltage from the LD drivingcircuit 2 is applied to the blue-violet semiconductor laser 1, it emitsblue-violet laser light having a wavelength of 400 to 410 nm, whichcorresponds to the HD DVD medium 21 (the thickness of a protective layer(of a second protective layer) is 0.6 mm) and the Blu-ray medium 20 (thethickness of a protective layer (of a first protective layer) is 0.075to 0.1 mm), onto the collimator lens 3. This blue-violet laser light isthe light that is linearly polarized in the X direction (firstdirection) parallel with the pn junction faces (hereinafter called Xdirection laser light (first laser light)). The X direction can beshifted by turning the blue-violet semiconductor laser 1 to allowselection of a desired polarizing direction. In this embodiment, anarrowed direction shown in FIG. 1 stands for the X direction to beunderstood in the further details.

The collimator lens 3 transforms the X direction laser light from theblue-violet semiconductor laser 1 into parallel light and emits theparallel right onto the liquid crystal element 4.

The liquid crystal element 4 consists of glass boards 12, 13 arranged tobe confronting each other, transparent electrodes 14, 15 placed on theinterior of the glass boards 12, 13, and a liquid crystal molecule layer16 made of liquid crystal molecules sealed in between the transparentelectrodes 14, 15. An ac voltage from the liquid crystal driving circuit5 is applied to the transparent electrodes 14, 15. This causes theliquid crystal molecules in the liquid crystal molecule layer 16 toshift in the direction correspondence to the level of the ac voltageapplied to the transparent electrodes 14, 15, resulting in a change inthe direction of an optical indicatrix. For instance, when an ac voltageV1 from the liquid crystal driving circuit 5 is applied to thetransparent electrodes 14, 15, the liquid crystal molecules shift in thedirection corresponding to the ac voltage V1, and, at this time, theoptical indicatrix given by the liquid crystal molecule layer 16 tiltsin such a direction that the indicatrix allows the X direction laserlight to pass through the liquid crystal molecule layer 16 whilemaintaining the original polarized direction, that is, in the directionthat the indicatrix gives the X direction laser light no phasedifference. On the other hand, when an ac voltage V2, lower than the acvoltage V1, from the liquid crystal driving circuit 5 is applied to thetransparent electrodes 14, 15, the liquid crystal molecules shift in thedirection corresponding to the ac voltage V2. At this time, the opticalindicatrix given by the liquid crystal molecule layer 16 tilts in such adirection that the indicatrix causes a phase difference of half of thewavelength between each component of the plane of polarization of the Xdirection laser light that is parallel with and perpendicular to themajor axis of the indicatrix. As a result, the X direction laser lightis subjected to a phase action as effective as one exerted by a halfwavelength plate in the polarizing direction, is transformed into thelight polarized in the Y direction (second direction perpendicular tothe page surface in FIG. 1) crossing the X direction at right angles(hereinafter referred to as Y direction laser light (second laserlight)), and comes out of the liquid crystal element 4.

A conventional technique to offer the same effect as the half wavelengthplate using liquid crystal is, for example, described in JP-A No.14-260272. While the liquid crystal element 4 is used to turn the Xdirection laser light into the Y direction laser light in thisembodiment, the crystal element 4 is not the only option for shiftingthe polarizing direction. For instance, a half wavelength plate made ofcrystal or a double refraction film, such as ARTON, can be employed. Toturn the X direction laser light into the Y direction laser light usinga half wavelength plate, the half wavelength plate is located on a lightpath for the X direction laser light, so that the X direction laserlight falling on the half wavelength plate is turned into the Ydirection laser light with the shifted polarization of Y direction. Tolet the X direction laser light pass through the liquid crystal element4, the half wavelength plate is not located on the light path for the Xdirection laser light, so that the X direction laser light is emittedonto the mirror 6 without being transformed.

The mirror 6 reflects the x direction laser light and Y direction laserlight from the liquid crystal element 4 to send them to the polarizinghologram element 8.

The polarizing hologram element 8 is made by sealing a double refractivematerial 17, such as liquid crystal or lithium niobate, with glassboards 7, 9. The hologram pattern shown in FIGS. 3, 4 is formed betweenthe double refractive material 17 and the glass board 9. Concentriccircles shown in FIG. 3 represent the plan view of the hologram patternon the incident side of the X direction laser light and Y directionlaser light (lower side in FIG. 1). Rectangles shown in FIG. 4 representthe sectional view that is given by cutting the hologram pattern seen inperpendicular to the page surface in FIG. 1 along the incident directionof the X direction laser light and Y direction laser light. The hologrampattern is formed in an NA 0.65 area (second area), which is inside anNA 0.85 area (first area) of the objective lens 10 that corresponds tothe Blu-ray medium 20.

The double refractive material 17 shows a refractive index n1, which isalmost equal to the refractive index ng of the glass boards 7, 9,against the X direction laser light. The X direction laser light,therefore, passes through the polarizing hologram element 8 withoutbeing diffracted as shown in FIG. 4, and proceeds to the objective lens10. The double refractive material 17, however, shows a refractive indexn2, which is different from the refractive index ng of the glass boards7, 9, against the Y direction laser light. Because of this, the Ydirection laser light is diffracted by the hologram pattern, thus turnedinto, for example, zero order light and ∓primary light as shown in FIG.4. In other words, the hologram pattern is so optimized that, forexample, the aberration of +primary light to the information surface ofthe HD DVD medium 21 becomes almost zero. This means that the hologrampattern is formed as the pattern that is determined unconditionally bysuch a factor as a gap between the polarizing hologram element 8, whichhas the hologram pattern, and the objective lens 10.

The lens holder 11 has an aperture limiting portion 18 that limits theincidence of the X direction laser light and Y direction laser light, sothat the laser converging apparatus 19 is provided with a limited NA0.85 adapted to the Blu-ray medium 20. The polarizing hologram element 8and the objective lens 10 are fixed to the lens holder 11 by ordinarymeans of gluing or known techniques of anchoring or fitting.

The objective lens 10 has the NA 0.85 and corresponds to the Blu-raymedium 20. The objective lens 10 so converges the X direction laserlight from the polarizing hologram element 8 that the X direction laserlight shows almost zero aberration to the information surface of theBlu-ray medium 20. Also, the objective lens 10 so converges the +primarylight from the polarizing hologram element 8 that the +primary lightshows almost zero aberration to the information surface of the HD DVDmedium 21.

=Operation of the Optical Pickup Device to Which the Laser ConvergingApparatus Applies=

(1) Operation of the Optical Pickup Device in Application to the Blu-rayMedium 20

The following is a description of the operation of the laser convergingapparatus 19 and the optical pickup device to which the laser convergingapparatus 19 applies according to the present invention, in applicationto the Blu-ray medium 20. The description will be made referring toFIGS. 1 to 4.

The Blu-ray medium 20 is an optical disk medium conforming to theBlu-ray standard specifying the protective layer thickness of 0.075 to0.1 mm. The Blu-ray medium 20 is held with a chucking mechanism on thefront end of a disk motor (no drawing is given), which revolves theBlu-ray medium 20 at a given linear velocity (or angular velocity).

When the optical pickup device starts operating, the LD driving circuit2 applies the control voltage to the blue-violet semiconductor laser 1,which in response emits the X direction laser light having thewavelength of 400 to 410 nm onto the collimator lens 3. The X directionlaser light turns is into parallel light while passing through thecollimator lens 3, and proceeds further to the liquid crystal element 4.The liquid crystal driving circuit 5 applies the ac voltage V1 to thetransparent electrodes 14, 15 when the optical pickup device startsoperating. In response, the liquid crystal molecules in the liquidcrystal molecule layer 16 shift in the direction corresponding to the acvoltage V1. As a result, the optical indicatrix of the liquid crystalmolecule layer 16 tilts in such a direction that the indicatrix allowsthe X direction laser light to pass through the liquid crystal element 4while maintaining the original polarizing direction. The X directionlaser light, therefore, passes through the glass board 12, the liquidcrystal molecule layer 16, and the glass board 13 to be incident on themirror 6. The X direction laser light is then reflected by the mirror 6,and is sent to the polarizing hologram element 8. The double refractivematerial 17 of the polarizing hologram element 8 shows the refractiveindex n1 equal to the refractive index ng of the glass boards 7, 9against the X direction laser light. Because of this, the X directionlaser light is not diffracted by the hologram pattern, and passesthrough glass board 7, the double refractive material 17, and the glassboard 9 in the NA 0.85 area to be incident on the objective lens 10 (seethe X direction laser light in FIG. 4). The X direction laser light isso converged by the objective lens 10 that X direction laser light showsalmost zero aberration to the information surface of the Blu-ray medium20. Hence the converged x direction laser light is projected on theinformation surface of the Blu-ray medium 20 to execute recording andreproduction on the Blu-ray medium 20 in a fine manner.

(2) Operation of the Optical Pickup Device in Application to the HD DVDMedium 21

The following is a description of the operation of the laser convergingapparatus 19 and the optical pickup device to which the laser convergingapparatus 19 applies according to the present invention, in applicationto the HD DVD medium 21. The description will be made referring to FIGS.2 to 9. FIG. 5 is a general block diagram for describing the operationof the optical pickup device shown in FIG. 1 in application to the HDDVD medium 21. FIG. 6 is a graphic diagram showing the exemplary stateof Y direction laser light in the laser converging apparatus 19 and theHD DVD medium 21. FIG. 7 is a graphic diagram showing a diffusionhologram pattern formed in the part of the NA 0.85 area other than an NA0.65 area. FIGS. 8, 9 are graphic diagrams showing other sectionalshapes of the hologram pattern.

The HD DVD medium 21 is an optical disk medium conforming to the HD DVDstandard specifying the protective layer thickness of 0.6 mm. Like theBlu-ray medium 20, the HD DVD medium 21 is held with the chuckingmechanism on the front end of the disk motor (no drawing is given),which revolves the HD DVD medium 21 at a given linear velocity (orangular velocity).

As described above, when the optical pickup device starts operating, theLD driving circuit 2 applies the control voltage to the blue-violet.semiconductor laser 1, which in response emits the X direction laserlight having the wavelength of 400 to 410 nm onto the collimator lens 3.The X direction laser light turns into parallel light while passingthrough the collimator lens 3, and proceeds further to the liquidcrystal element 4. The liquid crystal driving circuit 5 applies the acvoltage V1 to the transparent electrodes 14, 15 when the optical pickupdevice starts operating. In response, the liquid crystal molecules inthe liquid crystal molecule layer 16 shift in the directioncorresponding to the ac voltage V1. As a result, the optical indicatrixof the liquid crystal molecule layer 16 tilts in such a direction thatthe indicatrix allows the X direction laser light to pass through theliquid crystal element 4 while maintaining the original polarizingdirection. The X direction laser light, therefore, passes through theglass board 12, the liquid crystal molecule layer 16, and the glassboard 13 to be incident on the mirror 6. Hence the X direction laserlight is projected on the HD DVD medium 21 via the polarizing hologramelement 8 and the objective lens 10 in the same way as described above.

In this case, however, a spherical aberration occurs because of adifference in protective layer thicknesses between the Blu-ray medium 20and the HD DVD medium 21, and the liquid crystal driving circuit 5receives the information indicating the occurrence of the sphericalaberration. This information indicating the occurrence of the sphericalaberration, for example, represents the information (e.g. FE signal)that an optical detector or the like (no drawing) detects when itreceives the X direction laser light that is projected on theinformation surface of the HD DVD medium 21 to cause the sphericalaberration. Upon receiving the information, the liquid crystal drivingcircuit 5 applies the ac voltage V2 to the transparent electrodes 14,15, which in response causes the direction of the liquid crystalmolecules in the liquid crystal molecule layer 16 to shift in thedirection corresponding to the applied ac voltage V2. As a result, theoptical indicatrix of the liquid crystal molecule layer 16 tilts in sucha direction that the indicatrix acts on the X direction laser light as ahalf wavelength plate, and the polarizing direction of the X directionlaser light is shifted to the Y direction crossing the X direction atright angles. The Y direction laser light is, therefore, emitted fromthe liquid crystal element 4. The Y direction laser light is emittedonto the mirror 6 via the glass board 13, and is reflected by the mirror6 to further travel to the polarizing hologram element 8. The Ydirection laser light then passes through the glass board 7 in the NA0.85 area. The double refractive material 17 of the polarizing hologramelement 8 shows the refractive index n2 different from the refractiveindex ng of the glass boards 7, 9 against the Y direction laser light.Because of this, the Y direction laser light falling into the NA 0.65area inside the NA 0.85 area is diffracted by the hologram patternbetween the double refractive material 17 and the glass board 9 into,for example, zero order light and ∓primary light, and falls on theobjective lens 10 (see the Y direction laser light shown in FIG. 4). The+primary light is then so converged by the objective lens 10 that the+primary light shows almost zero aberration to the information surfaceof the HD DVD medium 21. Hence the converged +primary light is projectedon the information surface of the HD DVD medium 21 to execute recordingand reproduction on the HD DVD medium 21 in a fine manner.

The Y direction laser light having passed through the part of the NA0.85 area other than the NA 0.65 area (hereinafter referred to as Ydirection flare light) is not converged onto the information surface ofthe HD DVD medium 21 as shown in FIG. 6. The Y direction flare light,therefore, flares widely relative to the size of the optical detectorwhen an optical magnification for an outward path from the informationsurface of the HD DVD medium 21 to the optical detector is larger than agiven magnification, thus most part of the Y direction flare light doesnot fall on the detector. This ensures that the Y direction flare lightdoes not have an effect (a decline in the signal-to-noise ratio ofsignals from the information surface, a change in the waveforms of servosignals obtained from the signals, etc.) on recording and reproductionoperation on the HD DVD medium 21. On the other hand, when an opticalmagnification for a return path is smaller than a given magnificationdue to such a limitation as the size of an optical system, the Ydirection flare light may have an effect on recording and reproductionoperation on the HD DVD medium 21. To prevent that from happening, adiffusion hologram pattern is formed in the part of the NA 0.85 areaother than the NA 0.65 area. This diffusion hologram pattern convergesthe Y direction flare light into a location separated from theinformation surface of the 14D DVD medium 21 by a given distance ormore. The Y direction laser light is thus diffracted by the diffusionhologram pattern into, for example, zero order light and +primary light,and is converged into the location separated by the given distance.Hence the Y direction flare light comes to have less effect.

While the hologram pattern according to this embodiment has a sectionalshape of rectangles, as shown in FIG. 4, this is not the only option forthe sectional shape. As shown in FIG. 8, the sectional shape may be, forexample, a serration having approximately linear slopes in the directionof the optical axis of the Y direction laser light (hereinafter referredto as blaze shape), or, as shown in FIG. 9, may be a serration havingstepped slopes in the direction of the optical axis of the Y directionlaser light (hereinafter referred to as stepped blaze shape). Thehologram pattern having the section of the blaze shape or stepped blazeshape exerts greater efficiency in diffracting the +primary light fromthe Y direction laser light than the hologram pattern having the sectionof rectangles does. This enables the conversion of the +primary lightwith greater intensity onto the information surface of the HD DVD medium21, allowing recording on the HD DVD medium 21 at higher speed.

According to the embodiment described above, the X direction laser lighthaving passed through the NA0.85 area can be converged onto theinformation surface of the Blu-ray medium 20, and the +primary lighthaving passed through the NA0.65 area can be converged onto theinformation surface of the HD DVD medium 21. This enables one objectivelens 10 to serve for recording and reproduction on both optical diskmedia (Blu-ray medium 20 and HD DVD medium 21) to which the laser lightof the same wavelength of 400 to 410 nm is used and which have differentprotective layer thicknesses.

Also, according to the embodiment, the Y direction laser light fallinginto the part of NA0.85 area other than the 0.65 area can be diffractedinto zero order light and ∓primary light via the diffusion hologrampattern. This reduces the effect of the Y direction flare light onrecording and reproduction operation on the HD DVD medium 21.

In addition, giving the hologram pattern the section of blaze shape orstepped blaze shape allows the hologram pattern to exert greaterefficiency in diffracting the Y direction laser light. This increasesthe intensity of the +primary light, enabling recording on the HD DVDmedium 21 at higher speed.

The embodiment thus provides the optical pickup device that comprisesthe blue-violet semiconductor laser 1 that emits the X direction laserlight, the liquid crystal element 4, and the laser converging apparatus19 that can be used for both optical disk media (Blu-ray medium 20 andHD DVD medium 21) to which the laser light of the same wavelength of 400to 410 nm is used and have different protective layer thicknesses.

Second Embodiment

=An Example of the Overall Configuration of an Optical Pickup Device toWhich a Laser Converging Apparatus Applies 32

The following is a description of the overall configuration of the laserconverging apparatus (laser converging assembly) 22 and the opticalpickup device to which the laser converging apparatus 22 appliesaccording to the present invention. The description will be madereferring to FIGS. 3, 4, 10, 11, 13. FIG. 10 is a functional blockdiagram showing another example of the overall configuration of theoptical pickup device according to the invention. FIGS. 11, 13 are thedetail views of the objective lens 10 and a nonpolarizing hologramelement 24 shown in FIG. 10. The same elements illustrated in FIG. 10 asin FIG. 1 are given the same symbols to save extra explanation.

The optical pickup device comprises a blue-violet semiconductor laser 23(semiconductor laser), the LD driving circuit 2, the collimator lens 3,the mirror 6, and the laser converging apparatus 22. The laserconverging apparatus 22 includes the nonpolarizing hologram element 24,the objective lens 10, and the lens holder 11. No drawings are given inFIG. 10, showing the optical pickup device, for an optical system, suchas an optical detector, for detecting FE signals, TE signals, RFsignals, etc., an optical component, and an actuator for driving thelaser converging apparatus 22 in a direction of focusing or tracking,which are incorporated into an ordinary optical pickup device.

The blue-violet semiconductor laser 23 is, for example, composed ofdiodes consisting of p-type semiconductors and n-type semiconductorsjoined via pn junctions. When a control voltage from the LD drivingcircuit 2 is applied to the blue-violet semiconductor laser 23, it emitsblue-violet laser light having the wavelength of 400 to 410 nm, whichcorresponds to the HD DVD medium (second disk medium) 21 (the thicknessof the protective layer (of the second protective layer) is 0.6 mm) andthe Blu-ray medium (first disk medium) 20 (the thickness of theprotective layer (of the first protective layer) is 0.075 to 0.1 mm),onto the collimator lens 3. Different from the case in the firstembodiment, this blue-violet laser light may be polarized in otherdirections, such as a circular direction, than a linear direction.

The collimator lens 3 transforms the blue-violet laser light from theblue-violet semiconductor laser 23 into parallel light and emits theparallel light onto the mirror 6. The mirror 6 reflects the parallelblue-violet laser light to send it to the nonpolarizing hologram element24.

The nonpolarizing hologram element 24 is made of, for example, glass orplastic, and has a hologram pattern on the blue-violet laser lightincident side (lower side in FIG. 10). The hologram pattern is formed inthe NA 0.65 area (second area), which is inside the NA 0.85 area (firstarea) of the objective lens 10 corresponding to the Blu-ray medium 20,and is shaped into the concentric circles shown in FIG. 3 when seen fromthe lower side in FIG. 10. The rectangles shown in FIG. 4 represents thesectional shape that is given by cutting the hologram pattern seen inperpendicular to the page surface in FIG. 10 along the incidentdirection of the blue-violet laser light. The hologram pattern diffractsthe blue-violet laser light into, for example, zero order light and∓primary light, and is so optimized that, for example, the aberration ofthe +primary light to the information surface of the HD DVD medium 21becomes almost zero. This means that the hologram pattern is formed asthe pattern that is determined unconditionally by such a factor as a gapbetween the nonpolarizing hologram element 24, which has the hologrampattern, and the objective lens 10.

The lens holder 11 has the aperture limiting portion 18 to provide thelaser converging apparatus 22 with the limited NA 0.85 adapted to theBlu-ray medium 20. The nonpolarizing hologram element 24 and theobjective lens 10 are fixed to the lens holder 11 by ordinary means ofgluing or known techniques of anchoring or fitting.

The objective lens 10 has the NA 0.85 and corresponds to the Blu-raymedium 20. The objective lens 10 is so designed that the zero orderlight having permeated the NA0.65 area of the nonpolarizing hologramelement 24 and the laser light having permeated the part of the NA 0.85area other than the NA 0.65 area (hereinafter referred to as permeatedlaser light) show almost zero aberrations to the information surface ofthe Blu-ray medium 20. The objective lens 10, therefore, so convergesthe zero order light and the permeated laser light as to make theiraberration to the information surface of the Blu-ray medium 20 almostzero. Also, the objective lens 10 so converges the +primary light fromthe hologram pattern as to make the aberration of the +primary lightalmost zero to the information surface of the HD DVD medium 21.

=Operation of the Optical Pickup Device to Which the Laser ConvergingApparatus Applies=

(1) Operation of the Optical Pickup Device in Application to the Blu-rayMedium 20

The following is a description of the operation of the laser convergingapparatus :22 and the optical pickup device to which the laserconverging apparatus 22 applies according to the present invention, inapplication to the Blu-ray medium 20. The description will be madereferring to FIGS. 10, 11, 14. FIG. 14 is a graph depicting theintensity distribution of zero order light and permeated laser light. InFIG. 14, the intensity levels of the zero order light and permeatedlaser light are indicated vertically, so that the higher in FIG. 14, thegreater the indicated intensity level.

The Blu-ray medium 20 is an optical disk medium conforming to theBlu-ray standard specifying the protective layer thickness of 0.075 to0.1 mm. The Blu-ray medium 20 is held with the chucking mechanism on thefront end of the disk motor (no drawing is given), which revolves theBlu-ray medium 20 at a given linear velocity (or angular velocity).

When the optical pickup device starts operating, the LD driving circuit2 applies a control voltage to the blue-violet semiconductor Laser 23,which in response emits the blue-violet laser light having thewavelength of 400 to 410 nm onto the collimator lens 3. The blue-violetlaser light turns into parallel light while passing through thecollimator lens 3, and proceeds further to the mirror 6. The blue-violetlaser light is then reflected by the mirror 6, and is sent to thenonpolarizing hologram element 24. The blue-violet laser light fallinginto the NA0.65 area of the nonpolarizing hologram element 24 isdiffracted into zero order light and ∓primary light, and is emitted ontothe objective lens 10 (single-dot chain lines shown in FIG. 11).Meanwhile, the blue-violet laser light falling into the part of theNA0.85 area other than the NA0.65 area of the nonpolarizing hologramelement 24 permeates nonpolarizing hologram element 24 to become thepermeated laser light, and is emitted onto the objective lens 10 (brokenlines shown in FIG. 11). The zero order light and permeated laser lightare so converged by the objective lens 10 as to show almost zeroaberration to the information surface of the Blu-ray medium 20. Hencethe converged zero order light and the permeated laser light areprojected on the information surface of the Blu-ray medium 20 to executerecording and reproduction on the Blu-ray medium 20 in a fine manner.

The intensity level of the blue-violet laser light is reduced in theNA0.65 area into a level shown in FIG. 14 (the intensity level of thezero order light) as the intensity level of the ∓primary light isdeducted. In the NA0.85 area, which includes the intensity level of thepermeated laser light, overall intensity level of the blue-violet laserlight becomes approximately flat as shown in FIG. 14. Because of this,the light consisting of the permeated laser light and zero order lightconverged onto the information surface of the Blu-ray medium 20(hereinafter referred to as spot light) is made smaller than spot lighthaving an intensity level that is not approximately flat. This enablesmore accurate recording and reproduction on the Blu-ray medium 20.

(2) Operation of the Optical Pickup Device in Application to the HD DVDMedium 21

The following is a description of the operation of the laser convergingapparatus 22 and the optical pickup device to which the laser convergingapparatus 22 applies according to the present invention, in applicationto the HD DVD medium 21. The description will be made referring to FIGS.6, 8, 9, 12, 13, 15. FIG. 12 is a general block diagram for describingthe operation of the optical pickup device shown in FIG. 10 inapplication to the HD DVD medium 21. FIG. 15 is a graphic diagramshowing another form of the hologram pattern.

The HD DVD medium 21 is an optical disk medium conforming to the HD DVDstandard specifying the protective layer thickness of 0.6 mm. Like theBlu-ray medium 20, the HD DVD medium 21 is held with the chuckingmechanism on the front end of the disk motor (no drawing is given),which revolves the HD DVD medium 21 at a given linear velocity (orangular velocity).

When the optical pickup device starts operating, the LD driving circuit2 applies the control voltage to the blue-violet semiconductor laser 23,which in response emits the blue-violet laser light having thewavelength of 400 to 410 nm onto the collimator lens 3. The blue-violetlaser light turns into parallel light while passing through thecollimator lens 3, and is emitted onto the mirror 6. The blue-violetlaser light is then reflected by the mirror 6, and is sent to thenonpolarizing hologram element 24. The blue-violet laser light fallinginto the NA0.65 area of the nonpolarizing hologram element 24 isdiffracted into zero order light and ∓primary light, and the +primarylight is emitted onto the objective lens 10 (two-dot chain lines shownin FIG. 13). The +primary light is so converged by the objective lens 10as to show almost zero aberration to the information surface of the HDDVD medium 21. Hence the converged +primary light is projected on theinformation surface of the HD DVD medium 21 to execute recording andreproduction on the HD DVD medium 20 in a fine manner.

The blue-violet laser light having passed through the part of the NA0.85 area other than the NA 0.65 area (hereinafter referred to as flarelight) is not converged onto the information surface of the HD DVDmedium 21 as shown in FIG. 6 in the first embodiment. The flare light,therefore, flares widely relative to the size of the optical detectorwhen an optical magnification for an outward path from the informationsurface of the HD DVD medium 21 to the optical detector is larger than agiven magnification, thus most part of the flare light does not fall onthe detector. This ensures that the flare light does not have an effect(a decline in the signal-to-noise ratio of signals from the informationsurface, a change in the waveforms of servo signals obtained from thesignals, etc.) on recording and reproduction on the HD DVD medium 21. Onthe other hand, when an optical magnification for a return path issmaller than a given magnification due to such a limitation as the sizeof the optical system, the flare light may have an effect on recordingand reproduction on the HD DVD medium 21. To prevent that fromhappening, a diffusion hologram pattern, which has the same function asthe diffusion hologram pattern according to the first embodiment, isformed in the part of the NA 0.85 area other than the NA 0.65 area. As aresult, the blue-violet laser light is diffracted, for example, intozero order light and ∓primary light by the diffusion hologram pattern,and is converged into a location separated from the information surfaceby a given distance to reduce the effect of the flare right.

While the nonpolarizing hologram element 24 has the hologram pattern onthe blue-violet laser light incident side according to this embodiment,the location of the hologram pattern is not limited to this position.For example, as shown in FIG. 15, the hologram pattern may be formed onthe objective lens 10side. The hologram pattern formed on the objectivelens 10 side is located in a space enclosed with the objective lens 10,the lens holder 11, and the nonpolarizing hologram element 24. Theenclosed space can protect the hologram pattern from damage due to dust,flaws, etc. Hence more accurate recording and reproduction can becarried out on the Blu-ray medium 20 and the HD DVD medium 21.

The sectional shape of the hologram pattern according to this embodimentis not limited to rectangles. The section of the hologram pattern can bemade selectively into the blaze shape shown in FIG. 8 or the steppedblaze shape shown in FIG. 9, according to an application of the opticalpickup device (for example, reproduction only for the Blu-ray medium 20;both recording and reproduction for the HD DVD medium 21). An example ofthe sectional shapes of the hologram pattern corresponding toapplications of the optical pickup device is described below.

The optical pickup device, for example, may be for use in both recordingand reproduction on the Blu-ray medium 20, and in reproduction only onthe HD DVD medium 21. In this case, the hologram pattern is given thesectional shape of rectangles that diffracts the blue-violet laser light(intensity 100%) into, for example, zero order light having 80%intensity enabling both recording and reproduction, and into ∓primarylight having 10% intensity,enabling only reproduction. As the rectanglesmade deeper in the direction of optical axis of the blue-violet laserlight, the intensity of the ∓primary light increases while that of thezero order light decreases.

As a result, the zero order light of 80% intensity and the permeatedlaser light (100% intensity with no diffraction) having permeated thepart of the NA 0.85 area other than the NA0.65 area are projected ontothe information surface of the Blu-ray medium 20 to enable recording andreproduction. Meanwhile, the +primary light of 10% intensity isprojected onto the information surface of the HD DVD medium 21 to enablereproduction only.

In another case, the optical pickup device may be for use in recordingonly on the Blu-ray medium 20, and in both recording and reproduction onthe HD DVD medium 21. In this case, the hologram pattern is given thesection of blaze shape or stepped blaze shape that diffracts theblue-violet laser light (intensity 100%) into, for example, zero orderlight having 20% intensity enabling only reproduction, into +primarylight having 80% intensity enabling both recording and reproduction, andinto -primary light having 0% intensity. As the blaze shape or steppedblaze shape made deeper in the direction of optical axis of theblue-violet laser light, the intensity of the +primary light increases.

As a result, the zero order light of 20% intensity and the permeatedlaser light (100% intensity with no diffraction) having permeated thepart of the NA 0.85 area other than the NA0.65 area are projected ontothe information surface of the Blu-ray medium 20 to enable reproductiononly. Meanwhile, the +primary light of 80% intensity is projected ontothe information surface of the HD DVD medium 21 to enable both recordingand reproduction.

This embodiment makes it possible to converge the permeated laser lighthaving permeated the part of the NA 0.85 area other than the NA0.65 areaand the zero order light having permeated the NA0.65 area onto theinformation surface of the Blu-ray medium 20, and to converge the+primary light having permeated the NA0.65 area onto the informationsurface of the HD DVD medium 21.

As a result, one object lens 10 is capable of serving for both recordingand reproduction on the optical disk media (Blu-ray medium 20 and HD DVDmedium 21) to which the laser light of the same wavelengths (400 to 410nm) is used and which have different protective layer thicknesses.

Also, according to the embodiment, the blue-violet laser light fallinginto the part of the NA 0.85 area other than the NA0.65 area can bediffracted into the zero order light and the ∓primary light via thediffusion hologram pattern.

This reduces the effect of the flare light on the recording andreproduction on the HD DVD medium 21.

Besides, the hologram pattern is formed on the objective lens 10 side tobe inside the space enclosed with the nonpolarizing hologram element 24,the lens holder 11, and objective lens 10. This protects the hologrampattern from damage due to dust, flaws, etc.

Hence more accurate recording and reproduction operation can be carriedout on the Blu-ray medium 20 and the HD DVD medium 21.

The embodiment thus provides the optical pickup device that comprisesthe blue-violet semiconductor laser 23 that emits the blue-violet laserlight, and the laser converging apparatus 22 that can be used for bothoptical disk media (Blu-ray medium 20 and HD DVD medium 21) which havedifferent protective layer thicknesses.

Third Embodiment

=An Example of the Overall Configuration of an Optical Pickup Device toWhich a Laser Converging Apparatus Applies=

The following is a description of the overall configuration of the laserconverging apparatus (laser converging assembly) 29 and the opticalpickup device to which the laser converging apparatus 29 appliesaccording to the present invention. The description will be madereferring to FIGS. 3, 4, 9, and 16 to 18. FIG. 16 is a functional blockdiagram showing another example of the overall configuration of theoptical pickup device according to the present invention. FIG. 17 is adetail view of the objective lens 10, a nonpolarizing hologram element33, and a polarizing hologram element 30 shown in FIG. 16. FIG. 18 is adetail view of a hologram pattern formed on the nonpolarizing hologramelement 33 shown in FIG. 17. In the following description, an opticaldisk medium conforming to the DVD standard is referred to as DVD medium(third disk medium) 34. The same elements illustrated in FIG. 16 as inFIG. 1 are given the same symbols to save extra explanation.

The optical pickup device comprises the blue-violet semiconductor laser1 (first semiconductor laser), the LD driving circuit 2, the collimatorlens 3, the liquid crystal element 4 (polarization direction switchingelement), the liquid crystal driving circuit 5, a red semiconductorlaser (second semiconductor laser) 32, a LD driving circuit 31, acollimator lens 26 for red color, a dichroic mirror 27, a mirror 28, andthe laser converging apparatus 29. The laser converging apparatus 29includes the polarizing hologram element 30, nonpolarizing hologramelement 33, the objective lens 10, and the lens holder 11.

The semiconductor Laser 32 is, for example, composed of diodesconsisting of p-type semiconductors and n-type semiconductors joined viapn junctions. When a control voltage from the LD driving circuit 31 isapplied to the semiconductor laser 32, it emits red laser light having awavelength of 650 to 660 nm, which corresponds to the DVD medium 34 (thethickness of a protective layer (of a third protective layer) is 0.6mm), onto the collimator lens 26 for red color. This red laser light isthe light that is linearly polarized in the X direction (firstdirection) parallel with the pn junction faces (hereinafter referred toas X direction red laser light (third laser light)) to have the samepolarizing direction as the X direction laser light emitted by theviolet semiconductor laser 1. The X direction can be shifted by turningthe semiconductor laser 32 to allow selection of a desired polarizingdirection. In this embodiment, an arrowed direction shown in FIG. 16stands for the X direction to be understood in the further details.

The collimator lens 26 for red color transforms the X direction redlaser light into parallel light and emits the parallel right onto thedichroic mirror 27.

The dichroic mirror 27 reflects the X direction red laser light from thecollimator lens 26 for red color to send the X direction red laser lightto the mirror 28. The dichroic mirror 27 also transmits X directionlaser light (first laser light) and Y direction laser-light (secondlaser light) from the liquid crystal element 4 to allow them to fall onthe mirror 28.

The mirror 28 reflects the X direction red laser light, the X directionlaser light, and the Y direction laser light to send them to thepolarizing hologram element 30.

The polarizing hologram element 30 consists of the glass boards 7 andthe double refractive material 17, which are described in the firstembodiment. The hologram pattern shown in FIGS. 3, 4 (hereinafterreferred to as polarizing hologram pattern) is formed between the doublerefractive material 17 and the nonpolarizing hologram element 33. Thepolarizing hologram element 30, therefore, transmits the X directionlaser light and X direction red laser light without diffracting them,and diffracts the Y direction laser light as it passes through.

The nonpolarizing hologram element 33 is, for example, consists of theglass board 9 described in the first embodiment, and has a wavelengthselecting hologram pattern (hereinafter referred to as nonpolarizinghologram pattern), which diffracts the X direction red laser light, onthe objective lens 10 side of the glass board 9. This nonpolarizinghologram pattern is formed in an NA0.60-0.65 area (third area)corresponding to the DVD medium 34, and has the concentric circularshape as shown in FIG. 3, for example, when seen from the lower side inFIG. 16. The nonpolarizing hologram pattern seen in perpendicular to thepage surface in FIG. 16 exhibits a section of the stepped blaze shapeshown in FIG. 9 when cut along the incident direction of the X directionred laser light. The nonpolarizing hologram pattern diffracts the Xdirection red laser light into, for example, zero order light and+primary light (hereinafter +primary light is referred to as nonpolarized +primary light). The nonpolarizing hologram pattern has adepth d (FIG. 18) in the direction of the optical axis of the Xdirection laser light and the +primary light created by the diffractionof the Y direction laser light by the polarizing hologram pattern(hereinafter referred to as polarized +primary light). This depth d isinteger times the value given by [wavelength of X direction laser lightand polarized +primary light (400 to 410 nm)/(refractive index ofnonpolarizing hologram element 33-1)]. As a result, the nonpolarizinghologram pattern transmits the X direction laser light and the polarized+primary light without diffracting them. The depth d is determined bythe equation: d=m[λ/(n−1)], where m stands for an integer, λ for thewavelength of 400 to 410 nm, and n for the refractive index of thenonpolarizing hologram element 33 for the wavelength of 400 to 410 nm.The nonpolarizing hologram pattern is so optimized as to transmit the Xdirection light and the polarized +primary light and, for example, makethe aberration of the non polarized +primary light zero to theinformation surface of the DVD medium 34. This means that thenonpolarizing hologram pattern is formed as the pattern that isdetermined unconditionally by such a factor as a gap between thenonpolarizing hologram element 33, which has the nonpolarizing hologrampattern, and the objective lens 10.

While the polarizing hologram element 30 and the nonpolarizing hologramelement 33 are combined into an integral body as shown in FIGS. 16, 17,this is not the only option. The polarizing hologram element 30 andnonpolarizing hologram element 33 may be provided as separated units. Insuch a case, the polarizing hologram pattern is formed as the patternthat corresponds to such a factor as the distance between the polarizinghologram element 30 and the objective lens 10 so that the polarized+primary light shows almost zero aberration to the information surfaceof the HD DVD medium 21 (second disk medium). Meanwhile, thenonpolarizing hologram pattern is formed as the pattern that correspondsto such a factor as the distance between the nonpolarizing hologramelement 33 and the objective lens 10 so that the non polarized +primarylight shows almost zero aberration to the information surface of the DVDmedium 34.

The lens holder 11 so holds the polarizing hologram element 30, thenonpolarizing hologram element 33, and the objective lens 10 as to keepthem across the given gaps that correspond to the patterns of respectivehologram elements. The lens holder 11 has the aperture limiting portion18, which provides the laser converging apparatus 29 with the limited NA0.85 (first area) adapted to the Blu-ray medium 20. The polarizinghologram element 30, the nonpolarizing hologram element 33, and theobjective lens 10 are fixed to the lens holder 11 by ordinary means ofgluing or known techniques of anchoring or fitting.

The objective lens 10 has the NA 0.85 and corresponds to the Blu-raymedium 20. The objective lens 10 so converges the X direction laserlight from the nonpolarizing hologram element 33 that the X directionlaser light shows almost zero aberration to the information surface ofthe Blu-ray medium 20. Also, the objective lens 10 so converges thepolarized +primary light from the nonpolarizing hologram element 33 thatthe polarized +primary light shows almost zero aberration to theinformation surface of the HD DVD medium 21. Further, the objective lens10 so converges the non polarized +primary light from the nonpolarizinghologram element 33 that the non polarized +primary light shows almostzero aberration to the information surface of the DVD medium 34.

=Operation of the Optical Pickup Device to Which the Laser ConvergingApparatus Applies=

The following is a description of the operation of the laser convergingapparatus 29 and the optical pickup device to which the laser convergingapparatus 29 applies according to the present invention, in applicationto the DVD medium 34. The description will be made referring to FIGS. 6and 16 to 19. FIG. 19 is a graphic diagram showing another form of thenonpolarilzing hologram pattern. The operation of the optical pickupdevice in application to the Blu-ray medium 20 and the HD DVD medium 21is identical with that according to the first embodiment, and,therefore, is not described in the following.

The DVD medium 34 is an optical disk medium conforming to the DVDstandard specifying the protective layer thickness of 0.6 mm. The DVDmedium 34, like the Blu-ray medium 20 and the HD DVD medium 21, is heldwith the chucking mechanism on the front end of the disk motor (nodrawing is given), which revolves the DVD medium 34 at a given linearvelocity (or angular velocity).

When the optical pickup device starts operating, the LD driving circuit2 applies the control voltage to the blue-violet semiconductor laser 1,which in response emits the x direction laser light having thewavelength of 400 to 410 nm onto the collimator lens 3. The X directionlaser light turns into parallel light while passing through thecollimator lens 3, and proceeds further to the liquid crystal element 4.The liquid crystal driving circuit 5 applies the ac voltage V1 to thetransparent electrodes 14, 15 when the optical pickup device startsoperating. The liquid crystal molecules in the liquid crystal moleculelayer 16 shift in the direction corresponding to the ac voltage V1. As aresult, the optical indicatrix of the liquid crystal molecule layer 16tilts in such a direction that the indicatrix allows the X directionlaser light to pass through the liquid crystal element 4 whilemaintaining the original polarizing direction. The X direction laserlight, therefore, passes through the glass board 12, the liquid crystalmolecule layer 16, and the glass board 13 to be incident on the dichroicmirror 27. The X direction laser light passes through dichroic mirror 27to proceed to the mirror 28, which then reflects the incoming Xdirection laser light to send it to the polarizing hologram element 30.The X direction laser light passes through the polarizing hologramelement 30, as in the case of the polarizing hologram element accordingto the first embodiment, to fall on the nonpolarizing hologram element33. Since the depth d of the nonpolarizing hologram pattern of thenonpolarizing hologram element 33 is integer times the value given by[wavelength of X direction laser light (400 to 410 nm)/(refractive indexof nonpolarizing hologram element 33-1)], the X direction laser lightpasses through the nonpolarizing hologram element 33 without beingdiffracted by the nonpolarizing hologram pattern, and falls on theobjective lens 10. The X direction laser light is then converged by theobjective lens 10, and is emitted onto the DVD medium 34.

In this case, however, a spherical aberration occurs because of adifference in protective layer thicknesses between the Blu-ray medium 20and the DVD medium 34, and the liquid crystal driving circuit 5 receivesthe information indicating the occurrence of the spherical aberration.Upon receiving the information, the liquid crystal driving circuit 5applies the ac voltage V2 to the transparent electrodes 14, 15, which inresponse causes the direction of the liquid crystal molecules in theliquid crystal molecule layer 16 to shift in the direction correspondingto the applied ac voltage V2. As a result, the optical indicatrix of theliquid crystal molecule layer 16 tilts in such a direction that theindicatrix acts on the X direction laser light as a half wavelengthplate, and the polarizing direction of the X direction laser light isshifted to the Y direction crossing the X direction at right angles. TheY direction laser light is, therefore, emitted from the liquid crystalelement 4. The Y direction laser light is emitted onto the dichroicmirror 27, passing through the dichroic mirror 27, and falling on themirror 28, which reflects the Y direction laser light to send it to thepolarizing hologram element 30. The Y direction laser light isdiffracted by the polarizing hologram pattern as in the case of thefirst embodiment, and the polarized +primary light is then emitted ontothe nonpolarizing hologram pattern. Since the depth d of thenonpolarizing hologram pattern of the nonpolarizing hologram element 33is integer times the value given by [wavelength of polarized +primarylight (400 to 410 nm)/(refractive index of nonpolarizing hologramelement 33-1)], the polarized +primary light passes through thenonpolarizing hologram element 33 without being diffracted by thenonpolarizing hologram pattern, and falls on the objective lens 10. Thepolarized +primary light is then converged by the objective lens 10, andis emitted onto the DVD medium 34.

The DVD medium 34 is, however, designed for use with red laser lighthaving a wavelength of 650 to 660 nm. Because of this, a coloraberration or the like occurs when the polarized +primary light havingthe wavelength of 400 to 410 nm is projected on the DVD medium 34. TheLD driving circuit 2 and the LD driving circuit 31 receive informationindicating the occurrence of the aberration or the like. Thisinformation indicating the occurrence of the aberration or the like, forexample, represents the information that an optical detector or the like(no drawing) detects when it receives the polarized +primary light thatis projected on the information surface of the DVD medium 34 to causethe aberration or the like. Upon receiving the information, the LDdriving circuit 2 stops applying the control voltage to the blue-violetsemiconductor laser 1, while the LD driving circuit 31 applies thecontrol voltage to the semiconductor laser 32. A series of operations upto the application of the control voltage to the semiconductor laser 32is described as merely an instance, and do not exclude other options.For example, the optical pickup device may be provided with a modechangeover switch that has a Blu-ray medium 20 mode, a. HD DVD medium 21mode, a DVD medium 34 mode, etc. In this case, for example, a usermanually operates the mode changeover switch and switches on a desiredmode to make the LD driving circuit 31 apply the control voltage to thesemiconductor laser:32 upon startup of the optical pickup device.

Responding to the control voltage, the semiconductor laser 32 emits theX direction red laser light having the wavelength of 650 to 660 nm ontothe collimator lens 26 for red color. The X direction red laser lightturns into parallel light while passing through the collimator lens 26,and proceeds to the dichroic mirror 27. The X direction red laser lightis then reflected by the dichroic mirror 27 to fall on the mirror 28,and is reflected again by the mirror 28 to fall on the polarizinghologram element 30, where the X direction red laser light passesthrough the glass board 7 in the NA0.85 area. The double refractivematerial 17 of the polarizing hologram element 30 shows the refractiveindex n1 equal to the refractive index ng of the glass board 7 againstthe X direction red laser light. As a result, the X direction red laserlight passes through the glass board 7 and the double refractivematerial 17 without being diffracted by the polarizing hologram pattern,and proceeds to the nonpolarizing hologram element 33. The depth d ofthe nonpolarizing hologram pattern of the nonpolarizing hologram element33 is not integer times the value given by [wavelength of X directionred laser light (650 to 660 nm)/(refractive index of nonpolarizinghologram element 33-1)]. Because of this, the X direction red laserlight in the NA0.60-0.65 area is diffracted into zero order light and∓primary light by the nonpolarizing hologram pattern, and is emittedonto the objective lens 10. Subsequently, the non polarized +primarylight is so converged by the objective lens 10 as to show almost zeroaberration to the information surface of the DVD medium 34. Hence theconverged non polarized +primary light is projected on the informationsurface of the DVD medium 34 to execute recording and reproduction onthe DVD medium 34 in a fine manner.

While the nonpolarizing hologram pattern having the section of steppedblaze shape is used in this embodiment, the sectional shape to beadopted is not limited to this shape. For example, rectangles shown inFIG. 19 are also applicable as a sectional shape. The rectangles have adepth din the direction of optical axis of the X direction laser lightand polarized +primary light that is integer times the value given by[wavelength of X direction laser light and Y direction laser light (400to 410 nm)/(refractive index of nonpolarizing hologram element 33-1)].The reason for using the stepped blaze shape in this embodiment is thatthe nonpolarizing hologram pattern having the section of stepped blazeshape shows greater efficiency in diffracting the non polarized +primarylight, thus transmitting the X direction laser light and polarized+primary light without fail.

The Y direction flare light having passed through the part of the NA0.85 area other than the NA 0.65 area (second area) is not convergedonto the information surface of the HD DVD medium 21 as shown in FIG. 6of the first embodiment. The Y direction flare light, therefore, flareswidely relative to the size of the optical detector when an opticalmagnification for an outward path from the information surface of the HDDVD medium 21 to the optical detector is larger than a givenmagnification, thus most part of the Y direction flare light does notfall on the detector. This ensures that the Y direction flare light doesnot have an effect (a decline in the signal-to-noise ratio of signalsfrom the information surface, a change in the waveforms of servo signalsobtained from the signals, etc.) on recording and reproduction operationon the HD DVD medium 21. On the other hand, when an opticalmagnification for a return path is smaller than a given magnificationdue to such a limitation as the size of the optical system, the Ydirection flare light may have an effect on recording and reproductionoperation on the HD DVD medium 21. To prevent that from happening, adiffusion hologram pattern, which functions in the same way as thediffusion hologram pattern according to the first embodiment, is formedin the part of the NA 0.85 area other than the NA 0.65 area. As aresult, the Y direction laser light is diffracted by this diffusionhologram pattern into, for example, zero order light and ∓primary light,and is converged into a location separated from the information surfaceof the HD DVD medium 21 by a given distance or more. Hence the Ydirection flare light comes to have less effect.

The X direction red laser light having passed through the part of the NA0.85 area other than the NA 0.60-0.65 area (hereinafter referred to as Xdirection red flare light) is not converged onto the information surfaceof the DVD medium 34. The X direction red flare light, therefore, flareswidely relative to the size of the optical detector when an opticalmagnification for an outward path from the information surface of theDVD medium 34 to the optical detector is larger than a givenmagnification, thus most part of the X direction red flare light doesnot fall on the detector. This ensures that the X direction red flarelight does not have an effect (a decline in the signal-to-noise ratio ofsignals from the information surface, a change in the waveforms of servosignals obtained from the signals, etc.) on recording and reproductionoperation on the DVD medium 34. On the other hand, when an opticalmagnification for a return path is smaller than a given magnificationdue to such a limitation as the size of the optical system, the Xdirection red flare light may have an effect on recording andreproduction operation on the DVD medium 34. To prevent that fromhappening, a diffusion hologram pattern is formed on one surface of thenonpolarizing hologram element 33 that has the nonpolarizing hologrampattern (see FIG. 17) in the part of the NA0.85 area other than the NA0.60-0.65 area. This diffusion hologram pattern is so formed as toconverge the X direction red flare light into a location separated fromthe information surface of the DVD medium 34 by a given distance ormore. As a result, the X direction red laser light is diffracted by thediffusion hologram pattern into, for example, zero order light and∓primary light, and is converged into the location separated from theinformation surface of the DVD medium 34 by the given distance or more.Hence the X direction red flare light comes to have less effect.

According to the laser converging apparatus 29, though the polarizinghologram element 30 and the nonpolarizing hologram element 33 arearranged in increasing order in the incident direction of the Xdirection laser light or the like, other arrangement is also possible.The polarizing hologram element 30 and the nonpolarizing hologramelement 33 may be arranged in decreasing order in the incident directionof the X direction laser light or the like. In this case, the polarizinghologram pattern is so formed as to correspond to the distance betweenthe polarizing hologram element 30 and the objective lens 10 so that thepolarizing hologram pattern makes the aberration of the polarized+primary light almost zero to the information surface of the HD DVDmedium 21. Likewise, the nonpolarizing hologram pattern is so formed asto correspond to the distance between the nonpolarizing hologram element33 and the objective lens 10 so that the nonpolarizing hologram patternmakes the aberration of the non polarized +primary light almost zero tothe information surface of the DVD medium 34.

This embodiment enables the convergence of the X direction laser lighthaving passed through the NA0.85 area onto the information surface ofthe Blu-ray medium 20, convergence of the polarized +primary light fromthe polarizing hologram pattern in the NA0.65 area onto the informationsurface of the HD DVD medium 21, and convergence of the non polarized+primary light from the nonpolarizing hologram pattern in the NA0.6-0.65area onto the information surface of the DVD medium 34. According to theembodiment, therefore, one objective lens 10 is capable of serving forrecording and reproduction on both optical disk media (Blu-ray medium 20and HD DVD medium 21) to which the laser light of the same wavelength(400 to 410 nm) is used and which have different protective layerthicknesses, and on an optical disk medium (DVD medium 34) to which thelaser light of a different wavelength (650 to 660 nm) is used.

According to this embodiment, the X direction red laser light emittedfrom the semiconductor laser 32 can pass through the polarizing hologramelement 30 without being diffracted. Besides, the section of thenonpolarizing hologram pattern is made into the rectangles whose depth din the direction of optical axis of the X direction laser light and thepolarized +primary light is integer times the value given by [wavelengthof X direction laser light and polarized +primary light/(refractiveindex of nonpolarizing hologram element 33-1], or into the stepped blazeshape having the depth d of each step in the above direction of theoptical axis that is given by [(wavelength of X direction laser lightand polarized +primary light) X an integer/(refractive index ofnonpolarizing hologram element 33-1]. As a result, the nonpolarizinghologram pattern can transmit the X direction laser light and polarized+primary light without diffracting them, and diffract the X directionred laser light without fail.

Also, the diffusion hologram pattern can diffract the incident Ydirection laser light falling into the part of the NA0.85 area otherthan NA0.65 area into zero order light and ∓primary light. This reducesthe effect of the Y direction flare light on recording and reproductionon the HD DVD medium 21.

The embodiment thus provides the optical pickup device that comprisesthe blue-violet semiconductor laser 1 that emits the X direction laserlight, the liquid crystal element 4, the semiconductor laser 32 thatemits the X direction red laser light, and the laser convergingapparatus 29 that can be used for both optical disk media (Blu-raymedium 20 and HD DVD medium 21), to which the laser light of the samewavelength (400 to 410 nm) is used and which have different protectivelayer thicknesses, and also for an optical disk medium (DVD medium 34),to which the laser light of a different wavelength (650 to 660 nm) isused and which has a different protective layer thickness.

Fourth Embodiment

=An Example of the Overall Configuration of an Optical Pickup Device toWhich a Laser Converging Apparatus Applies=

The following is a description of the overall configuration of the laserconverging apparatus (laser converging assembly) 35 and the opticalpickup device to which the laser converging apparatus 35 appliesaccording to the present invention. The description will be madereferring to FIGS. 3, 9, 20, 21. FIG. 20 is a functional block diagramshowing still another example of the overall configuration of theoptical pickup device according to the present invention. FIG. 21 is adetail view of the objective lens 10 and a nonpolarizing hologramelement 36 shown in FIG. 20. The same elements illustrated in FIG. 20 asin FIGS. 10, 16 are given the same symbols to save extra explanation.

The optical pickup device comprises the semiconductor laser 23 (firstsemiconductor laser), the LD driving circuit 2, the collimator lens 3, ared semiconductor laser (second semiconductor laser) 37, the LD drivingcircuit 31, a collimator lens 38 for red color, a dichroic mirror 39, amirror 40, and the laser converging apparatus 35. The laser convergingapparatus 35 includes the nonpolarizing hologram element (firstnonpolarizing hologram element and second nonpolarizing hologramelement) 36, the objective lens 10, and the lens holder 11.

The semiconductor laser 37 is, for example, composed of diodesconsisting of p-type semiconductors and n-type semiconductors joined viapn junctions. When a control voltage from the LD driving circuit 31 isapplied to the semiconductor laser 37, it emits red laser light havingthe wavelength of 650 to 660 nm (second laser light) onto the collimatorlens 38 for red color. This red laser light is applicable to the DVDmedium (third disk medium) 34 having the protective layer (thirdprotective layer) of 0.6 mm thick. Different from the applicationaccording to the third embodiment, the red laser light is not limited tothe laser light that is linearly polarized, but may be one that ispolarized circularly or in other direction.

The collimator lens 38 for red color transforms the red laser light intoparallel light, and emits the parallel light onto the dichroic mirror39, which then reflects the parallel red laser light from collimatorlens 38 to send it to the mirror 40. The dichroic mirror 39 alsotransmits the blue-violet laser light (first laser light) from thecollimator lens 3 to allow the blue-violet laser light: to proceed tothe mirror 40. The mirror 40 reflects the red laser light and theblue-violet laser light to send them to the nonpolarizing hologramelement 36.

The nonpolarizing hologram element 36 consists of the nonpolarizinghologram element 24 having the hologram pattern for diffracting theblue-violet laser light (hereinafter referred to as first nonpolarizinghologram pattern (first hologram pattern)) as described in the secondembodiment. The first nonpolarizing hologram pattern has a depth in thedirection of optical axis of the red laser light that is integer timesthe value given by [wavelength of red laser light (650 to 660nm)/(refractive index of nonpolarizing hologram element 36-1)]. Becauseof this, first nonpolarizing hologram pattern transmits the red laserlight without diffracting it.

The nonpolarizing hologram element 36 also has a hologram pattern fordiffracting the red laser light (hereinafter referred to as secondnonpolarizing hologram pattern (second hologram pattern)) on theobjective lens 10 side. This second hologram pattern is formed in theNA0.60-0.65 area (third area) corresponding to the DVD medium 34, andhas the concentric circular shape as shown in FIG. 3, for example, whenseen from the lower side in FIG. 20. The second nonpolarizing hologrampattern has a section of the stepped blaze shape shown in FIG. 9 that isgiven by cutting the second nonpolarizing hologram pattern seen inperpendicular to the page surface in FIG. 20 along the incidentdirection of the red laser light. The second nonpolarizing hologrampattern diffracts the red laser light into, for example, zero orderlight and ∓primary light (hereinafter this +primary light is referred toas second +primary light (second high-order diffracted light)). Thesecond nonpolarizing hologram pattern has a specific depth d in thedirection of the optical axis of the zero order light, +primary light(hereinafter this +primary light is referred to as first +primary light(first high-order diffracted light) ), which are created by thediffraction of the blue-violet laser light via the first nonpolarizinghologram pattern, and permeated laser light. This specific depth d isgiven by [(wavelength of zero order light, first +primary light, andpermeated light (400 to 410 nm))×an integer/(refractive index ofnonpolarizing hologram element 36-1)]. As a result, the secondnonpolarizing hologram pattern transmits the zero order light, first+primary light, and permeated light without diffracting them. In otherwords, the second nonpolarizing hologram pattern is so optimized as totransmit the zero order light, first +primary light, and permeatedlight, and, for example, make the aberration of the second +primarylight zero to the information surface of the DVD medium 34. This meansthat second nonpolarizing hologram pattern is formed as the pattern thatis determined unconditionally by such a factor as a gap between thenonpolarizing hologram element 36, which has the second nonpolarizinghologram pattern, and the objective lens 10.

While the first nonpolarizing hologram pattern and the secondnonpolarizing hologram pattern are formed integrally in thenonpolarizing hologram element 36, this is not the only option. A firstnonpolarizing hologram element (no drawing) having the firstnonpolarizing hologram pattern and a second nonpolarizing hologramelement (no drawing) having the second nonpolarizing hologram patternmay be provided as individual units. Both nonpolarizing hologramelements then may be combined into an integral unit, or arranged asrespective separate units. In this case, the first nonpolarizinghologram pattern is formed as the pattern that corresponds to thedistance between the first nonpolarizing hologram element and theobjective lens 10 so that the first +primary light shows almost zeroaberration to the information surface of the HD DVD medium (second diskmedium) 21. Meanwhile, the second nonpolarizing hologram pattern isformed as the pattern that corresponds to the distance between thesecond nonpolarizing hologram element and the objective lens 10 so thatthe second +primary light shows almost zero aberration to theinformation surface of the DVD medium 34.

The lens holder 11 so holds the nonpolarizing hologram element 36 andthe objective lens 10 as to keep the hologram element 36 and theobjective lens 10 across a given gap. The lens holder 11 has theaperture limiting portion 18, which provides the laser convergingapparatus 35 with the limited NA 0.85 (first area) adapted to theBlu-ray medium 20. The nonpolarizing hologram element 36 and theobjective lens 10 are fixed to the lens holder 11 by ordinary means ofgluing or known techniques of anchoring or fitting.

The objective lens 10 has the NA 0.85 and corresponds to the Blu-raymedium 20. The objective lens 10 so converges the zero order light andpermeated light from the nonpolarizing hologram element 36 that the zeroorder light and permeated light show almost zero aberration to theinformation surface of the Blu-ray medium 20. Also, the objective lens10 so converges the first +primary light from the nonpolarizing hologramelement 36 that the first +primary light shows almost zero aberration tothe information surface of the HD DVD medium 21. Further, the objectivelens 10 so converges the second +primary light from the nonpolarizinghologram element 36 that the second +primary light shows almost zeroaberration to the information surface of the DVD medium 34.

=Operation of the Optical Pickup Device to Which the Laser ConvergingApparatus Applies=

The following is a description of the operation of the laser convergingapparatus 35 and the optical pickup device to which the laser convergingapparatus 35 applies according to the present invention. The descriptionwill be made referring to FIGS. 11, 13, 20, 21. The operation of theoptical pickup device in application to the Blu-ray medium 20 and the HDDVD medium 21 is the same as described in the second embodiment, and,therefore, is not described further in the following.

The DVD medium 34 is an optical disk medium conforming to the DVDstandard specifying the protective layer thickness of 0.6 mm. The DVDmedium 34, like the Blu-ray medium 20 and the HD DVD medium 21, is heldwith the chucking mechanism on the front end of the disk motor (nodrawing is given), which revolves the DVD medium 34 at a given linearvelocity (or angular velocity).

When the optical pickup device starts operating, the LD driving circuit2 applies a control voltage to the blue-violet semiconductor laser 23,which in response emits the blue-violet laser light having thewavelength of 400 to 410 nm onto the collimator lens 3. The blue-violetlaser light turns into parallel light while passing through thecollimator lens 3, and proceeds further to the dichroic mirror 39, thenpasses through the dichroic mirror 39 to fall on the mirror 40. Theblue-violet laser light is reflected by the mirror 40 to fall on thenonpolarizing hologram element 36. The incident blue-violet laser lightfalling into the NA0.65 area (second area) of the nonpolarizing hologramelement 36 is diffracted into zero order light and +primary light by thefirst nonpolarizing hologram pattern, as in the case of the secondembodiment, and the zero order light is emitted onto the secondnonpolarizing hologram pattern (see the single-dot chain lines in FIG.11). Meanwhile, the blue-violet laser light falling into the part of theNA0.85 area other than the NA0.65 area of the nonpolarizing hologramelement 36 permeates nonpolarizing hologram element 36 to become thepermeated laser light, and is emitted onto the second nonpolarizinghologram pattern (see the broken lines shown in FIG. 11). Since thedepth of the second nonpolarizing hologram pattern is integer times thevalue given by [wavelength of blue-violet laser light (400 to 410nm)/(refractive index of nonpolarizing hologram element 36-1)], the zeroorder light and the permeated laser light pass through the nonpolarizinghologram element 36 without being diffracted by the second nonpolarizinghologram pattern, and falls on the objective lens 10. The zero orderlight and permeated laser light are then converged by the objective lens10, and are emitted onto the DVD medium 34. Likewise, the first +primarylight is converged by the objective lens 10, and is emitted onto the DVDmedium 34.

In this case, however, a spherical aberration occurs because the Blu-raymedium 20 and the DVD medium 34 have different protective layerthicknesses. In addition, since the DVD medium 34 is designed for usewith the red laser light having the wavelength of 650 to 660 nm, a coloraberration or the like results when the first +primary light having thewavelength of 400 to 410 nm is projected on the DVD medium 34. The LDdriving circuit 2 and the LD driving circuit 31 receive informationindicating the occurrence of the aberration or the like. Thisinformation indicating the occurrence of the aberration or the like, forexample, represents the information that the optical detector or thelike (no drawing) detects when it receives the zero order light andpermeated laser light and/or first +primary light that are projected onthe information surface of the DVD medium 34 to cause the aberration orthe like. Upon receiving the information, the LD driving circuit 2 stopsapplying the control voltage to the blue-violet semiconductor laser 23,while the LD driving circuit 31 applies the control voltage to thesemiconductor laser 37. A series of operations up to the application ofthe control voltage to the semiconductor laser 37 is described as merelyan instance, and do not exclude other options. For example, the opticalpickup device may be provided with the mode changeover switch that hasthe Blu-ray medium 20 mode, the HD DVD medium 21 mode, the DVD medium 34mode, etc. In this case, for example, a user manually operates the modechangeover switch and switches on a desired mode to make the LD drivingcircuit 31 apply the control voltage to the semiconductor laser 37 uponstartup of the optical pickup device.

Responding to the control voltage, the semiconductor laser 37 emits thered laser light having the wavelength of 650 to 660 nm onto thecollimator lens 38 for red color. The red laser light turns intoparallel light while passing through the collimator lens 38, andproceeds to the dichroic mirror 39. The red laser light is thenreflected by the dichroic mirror 39 to fall on the mirror 40, and isreflected again by the mirror 40 to fall on the nonpolarizing hologramelement 36.

Since the depth of the first nonpolarizing hologram pattern of thenonpolarizing hologram element 36 is integer times the wavelength of 650to 660 nm of the red laser light, the red laser light passes through thenonpolarizing hologram element 36 without being diffracted by the firstnonpolarizing hologram pattern, and falls on the second nonpolarizinghologram pattern. On the other hand, the depth of the secondnonpolarizing hologram pattern is not integer times the value given by[wavelength of red laser light (650 to 660 nm)/(refractive index ofnonpolarizing hologram element 36-1)], the red laser light in theNA0.60-0.65 area is diffracted into the zero order light and ∓primarylight by the second nonpolarizing hologram pattern, and is emitted onthe objective lens 10. The second +primary light is then so converged bythe objective lens 10 as to show almost no aberration to the informationsurface of the DVD medium 34. As a result, the converged second +primarylight is projected on the information surface of the DVD medium 34 toexecute recording and reproduction on the DVD medium 34 in a finemanner.

While the second nonpolarizing hologram pattern having the section ofstepped blaze shape is used in this embodiment, the sectional shape tobe adopted is not limited to this shape. For example, such rectanglesare also applicable that the rectangles have a depth d in the directionof optical axis of the zero order light, permeated laser light, andfirst +primary light that is integer times the value given by[wavelength of zero order light, permeated laser light, and first+primary light (400 to 410 nm)/(refractive index of nonpolarizinghologram element 36-1)]. The reason for using the stepped blaze shape inthis embodiment is that the second nonpolarizing hologram pattern havingthe section of stepped blaze shape shows greater efficiency indiffracting the second +primary light, thus transmits the zero orderlight, permeated laser light, and first +primary light without fail.Likewise, the first nonpolarizing hologram pattern can be formedselectively to have a section of rectangles or stepped blaze shape.

The flare light having passed through the part of the NA 0.85 area otherthan the NA 0.65 area is not converged onto the information surface ofthe HD DVD medium 21 as shown in FIG. 6 of the first embodiment. Theflare light, therefore, flares widely relative to the size of theoptical detector when an optical magnification for an outward path fromthe information surface of the HD DVD medium 21 to the optical detectoris larger than a given magnification, thus most part of the flare lightdoes not fall on the detector. This ensures that the flare light doesnot have an effect (a decline in the signal-to-noise ratio of signalsfrom the information surface, a change in the waveforms of servo signalsobtained from the signals, etc.) on recording and reproduction operationon the HD DVD medium 21. On the other hand, when an opticalmagnification for a return path is smaller than a given magnificationdue to such a limitation as the size of the optical system, the flarelight may have an effect on recording and reproduction operation on theHD DVD medium 21. To prevent that from happening, a diffusion hologrampattern, which functions in the same way as the diffusion hologrampattern according to the first embodiment, is formed in the part of theNA 0.85 area other than the NA 0.65 area. As a result, the blue-violetlaser light is diffracted by this diffusion hologram pattern into, forexample, zero order light and ∓primary light, and is converged into alocation separated from the information surface of the HD DVD medium 21by a given distance or more. Hence the flare light comes to have lesseffect.

The red laser light having passed through the part of the NA 0.85 areaother than the NA 0.60-0.65 area (hereinafter referred to as red flarelight) is not converged onto the information surface of the DVD medium34. The red flare light, therefore, flares widely relative to the sizeof the optical detector when an optical magnification for an outwardpath from the information surface of the DVD medium 34 to the opticaldetector is larger than a given magnification, thus most part of the redflare light does not fall on the optical detector. This ensures that thered flare light does not have an effect (a decline in thesignal-to-noise ratio of signals from the information surface, a changein the waveforms of servo signals obtained from the signals, etc.) onrecording and reproduction operation on the DVD medium 34. On the otherhand, when an optical magnification for a return path is smaller than agiven magnification due to such a limitation as the size of the opticalsystem, the red flare light may have an effect on recording andreproduction operation on the DVD medium 34. To prevent that fromhappening, a diffusion hologram pattern is formed on one surface of thenonpolarizing hologram element 36 that has the second nonpolarizinghologram pattern (see FIG. 21) in the part of the NA0.85 area other thanthe NA 0.60-0.65 area. This diffusion hologram pattern is so formed asto converge the red flare light into a location separated from theinformation surface of the DVD medium 34 by a given distance or more. Asa result, the red laser light is diffracted by the diffusion hologrampattern into, for example, zero order light and ∓primary light, and isconverged into the location separated from the information surface ofthe DVD medium 34 by the given distance or more. Hence the red flarelight comes to have less effect.

According to the laser converging apparatus 36, though the firstnonpolarizing hologram pattern and the second nonpolarizing hologrampattern are arranged in increasing order in the incident direction ofthe blue-violet laser light, other arrangement is also possible. Thefirst nonpolarizing hologram pattern and the second nonpolarizinghologram pattern may be arranged in decreasing order in the incidentdirection of the blue-violet laser light. In this case, the firstnonpolarizing hologram pattern is so formed as to correspond to thedistance between the first nonpolarizing hologram pattern and theobjective lens 10 so that the first nonpolarizing hologram pattern makesthe aberration of the first +primary light almost zero to theinformation surface of the HD DVD medium 21. Likewise, the secondnonpolarizing hologram pattern is so formed as to correspond to thedistance between the second nonpolarizing hologram pattern and theobjective lens 10 so that the second nonpolarizing hologram patternmakes the aberration of the second +primary light almost zero to theinformation surface of the DVD medium 34.

This embodiment enables the convergence of the permeated laser light andzero order light that have permeated the part of the NA0.85 area otherthan the NA0.65 area onto the information surface of the Blu-ray medium20, the convergence of the first +primary light from the firstnonpolarizing hologram pattern in the NA0.65 area onto the informationsurface of the HD DVD medium 21, and the convergence of the second+primary light from the second nonpolarizing hologram pattern in theNA0.60-0.65 area onto the information surface of the DVD medium 34.According to the embodiment, therefore, one objective lens 10 is capableof serving for recording and reproduction on both optical disk media(Blu-ray medium 20 and HD DVD medium 21), to which the laser light ofthe same wavelength (400 to 410 nm) is used and which have differentprotective layer thicknesses, and on an optical disk medium (DVD medium34), to which the laser light of a different wavelength (650 to 660 nm)is used.

According to this embodiment, the section of the first nonpolarizinghologram pattern is made into the rectangles whose depth in thedirection of optical axis of the red laser light is given by [wavelengthof red laser light/(refractive index of nonpolarizing hologram element36-1], or into the stepped blaze shape having the depth of each step inthe above direction of the optical axis that is integer times the valuegiven by [wavelength of red laser light/(refractive index ofnonpolarizing hologram element 36-1]. As a result, the firstnonpolarizing hologram pattern can transmit the red laser light withoutdiffracting it, and diffract the blue-violet laser light without fail.In addition, the section of the second nonpolarizing hologram pattern ismade into the rectangles whose depth in the direction of optical axis ofthe zero order light, permeated laser light, and first +primary light isinteger times the value given by [wavelength of zero order light,permeated laser light, and first +primary light/(refractive index ofnonpolarizing hologram element 36-1], or made into the stepped blazeshape having the depth of each step in the above direction of theoptical axis that is integer times the value given by [wavelength ofzero order light, permeated laser light, and first +primarylight/(refractive index of nonpolarizing hologram element 36-1]. As aresult, the second nonpolarizing hologram pattern can transmit the zeroorder light, permeated laser light, and first +primary light withoutdiffracting them, and diffract the red laser light without fail.

Also, the diffusion hologram pattern can diffract the incidentblue-violet laser light falling into the part of the NA0.85 area otherthan NA0.65 area into zero order light and ∓primary light. This reducesthe effect of the flare light on recording and reproduction on the HDDVD medium 21.

The embodiment thus provides the optical pickup device that comprisesthe blue-violet semiconductor laser 23 that emits the blue-violet laserlight, the semiconductor laser 37 that emits the red laser light, andthe laser converging apparatus 35 that can be used for both optical diskmedia (Blu-ray medium 20 and HD DVD medium 21), to which the laser lightof the same wavelength (400 to 410 nm) is used and which have differentprotective layer thicknesses, and also for an optical disk medium (DVDmedium 34), to which the laser light of a different wavelength (650 to660 nm) is used and which has a different protective layer thickness.

The above description of the third and fourth embodiments relates to thelaser converging apparatuses 29, 35 and the optical pickup devices towhich the laser converging apparatuses 29, 35 apply, in application tothe DVD medium 34. The laser converging apparatuses 29, 35 and theoptical pickup devices are also applicable to other media than the DVDmedium 34, such as an optical disk medium conforming to the CD standard(hereinafter referred to as CD medium), in other embodiments.

In such an embodiment, the semiconductor laser 32 (37) is replaced witha semiconductor laser that emits infrared laser having a wavelength of780 to 790 nm corresponding to the CD medium (with a protective layer of1.2 mm). In addition, a hologram pattern corresponding to the CD mediumis formed in an NA0.45-0.50 area of the nonpolarizing hologram element33 (nonpolarizing hologram element 36). This hologram pattern diffractsthe infrared laser light into, for example, zero light and ∓primarylight, and transmits blue-violet laser light. In other words, thehologram pattern is so optimized as to transmit the blue-violet laserlight and, for example, make the aberration of the +primary light zeroto the information surface of the CD medium. This means that thehologram pattern is determined unconditionally by such a factor as a gapbetween the nonpolarizing hologram element 33 (36) and the objectivelens 10. In this embodiment, the laser converging apparatuses 29, 35 andthe optical pickup devices operate as in the case of the third andfourth embodiments to enable fine recording and reproduction on the C1)medium.

While the description of the above embodiments relates to the laserconverging apparatuses and the optical pickup devices to which the laserconverging apparatuses apply, an optical disk recording/reproducingapparatus equipped with the laser converging apparatus or the opticalpickup device is also capable of the operation and effects that areexplained in the above embodiments.

The description concerning the laser converging apparatuses and theoptical pickup devices is made heretofore to facilitate understanding ofthe present invention, and is not made to limit the scope of the presentinvention. The present invention can be modified or improved withoutdeparting from the spirit of the invention, and encompasses equivalentsto the present invention.

1. A laser converging apparatus comprising: a polarizing hologramelement having a first area defined by a numerical aperturecorresponding to a thickness of a first protective layer of a first diskmedium and a second area inside the first area, the second area definedby a numerical aperture corresponding to a thickness of a secondprotective layer (>the thickness of the first protective layer) of asecond disk medium, the second area having a hologram pattern fortransmitting first laser light linearly polarized in a first directionwithout diffracting the first laser light while diffracting andtransmitting second laser light that is linearly polarized in a seconddirection crossing the first direction, the second laser light havingthe same wavelength as the first laser light; an objective lens havingthe numerical aperture corresponding to the thickness of the firstprotective layer, the objective lens converging the first laser lighthaving passed through the first area including the second area onto aninformation surface on one side of the first protective layer, theobjective lens converging the second laser light having passed throughthe second area onto an information surface on one side of the secondprotective layer; and a holder that holds the polarizing hologramelement and the objective lens.
 2. The laser converging apparatusaccording to claim 1, wherein the polarizing hologram element has adiffusion hologram pattern in a part of the first area other than thesecond area, the diffusion hologram pattern transmitting the first laserlight without diffracting the first laser light and diffracting thesecond laser light so that the second laser light having passed throughthe part of the first area other than the second area is not convergedonto the information surface on one side of the second protective layer.3. The laser converging apparatus according to claim 1, wherein thehologram pattern has a sectional shape in a direction of optical axis ofthe second laser light, the sectional shape being a serration havingsubstantially linear or stepped slopes.
 4. An optical pickup devicecomprising: (1) a semiconductor laser that emits a first laser lightpolarized linearly in a first direction; (2) a polarizing directionswitching element that transmits the first laser light while maintaininga polarizing direction of the first laser light or that transmits asecond laser light created by turning the polarizing direction of thefirst laser light to a second direction crossing the first direction;and (3) a laser converging assembly including: a polarizing hologramelement having a first area defined by a numerical aperturecorresponding to a thickness of a first protective layer of a first diskmedium and a second area inside the first area, the second area definedby a numerical aperture corresponding to a thickness of a secondprotective layer (>the thickness of the first protective layer) of asecond disk medium, the second area having a hologram pattern fortransmitting the first laser light without diffracting the first laserlight while diffracting and transmitting the second laser light; anobjective lens having the numerical aperture corresponding to thethickness of the first protective layer, the objective lens convergingthe first laser light having passed through the first area including thesecond area onto an information surface on one side of the firstprotective layer, the objective lens converging the second laser lighthaving passed through the second area onto an information surface on oneside of the second protective layer; and a holder that holds thepolarizing hologram element and the objective lens.
 5. A laserconverging apparatus comprising: a nonpolarizing hologram element havinga first area defined by a numerical aperture corresponding to athickness of a first protective layer of a first disk medium and asecond area inside the first area, the second area defined by anumerical aperture corresponding to a thickness of a second protectivelayer (>the thickness of the first protective layer) of a second diskmedium, the second area having a hologram pattern for diffracting laserlight into zero order light and high-order diffracted light having theorder of primary or higher; an objective lens having the numericalaperture corresponding to the thickness of the first protective layer,the objective lens converging the laser light having passed through apart of the first area other than the second area and the zero orderlight having passed through the second area onto an information surfaceon one side of the first protective layer, the objective lens convergingthe high-order diffracted light having passed through the second areaonto an information surface on one side of the second protective layer;and a holder that holds the nonpolarizing hologram element and theobjective lens.
 6. The laser converging apparatus according to claim 5,wherein the nonpolarizing hologram element has a diffusion hologrampattern in a part of the first area other than the second area, thediffusion hologram pattern diffracting the laser light having passedthrough the part of the first area other than the second area into zeroorder light and high-order diffracted light having the order of primaryor higher so that the laser light is not converged onto the informationsurface on one side of the second protective layer.
 7. The laserconverging apparatus according to claim 5, wherein the nonpolarizinghologram element has the hologram pattern on either a nonpolarizinghologram element surface confronting the objective lens or anonpolarizing hologram element surface not confronting the objectivelens.
 8. An optical pickup device comprising: (1) a semiconductor laserthat emits laser light; and (2) a laser converging assembly including: anonpolarizing hologram element having a first area defined by anumerical aperture corresponding to a thickness of a first protectivelayer of a first disk medium and a second area inside the first area,the second area defined by a numerical aperture corresponding to athickness of a second protective layer (>the thickness of the firstprotective layer) of a second disk medium, the second area having ahologram pattern for diffracting the laser light into zero order lightand high-order diffracted light having the order of primary or higher;an objective lens having the numerical aperture corresponding to thethickness of the first protective layer, the objective lens convergingthe laser light having passed through a part of the first area otherthan the second area and the zero order light having passed through thesecond area onto an information surface on one side of the firstprotective layer, the objective lens converging the high-orderdiffracted light having passed through the second area onto aninformation surface on one side of the second protective layer; and aholder that holds the nonpolarizing hologram element and the objectivelens.
 9. A laser converging apparatus comprising: a polarizing hologramelement having a first area defined by a numerical aperturecorresponding to a thickness of a first protective layer of a first diskmedium and a second area inside the first area, the second area definedby a numerical aperture corresponding to a thickness of a secondprotective layer (>the thickness of the first protective layer) of asecond disk medium, the second area having a polarizing hologram patternfor transmitting first laser light linearly polarized in a firstdirection without diffracting the first laser light, diffracting andtransmitting second laser light that is linearly polarized in a seconddirection crossing the first direction, the second laser light havingthe same wavelength as the first laser light, and transmitting thirdlaser light having a wavelength different from that of the first andsecond laser light without diffracting the third laser light; awavelength selecting nonpolarizing hologram element having a third areadefined by a numerical aperture corresponding to a thickness of a thirdprotective layer (>the thickness of the first protective layer) of athird disk medium, the third area having a nonpolarizing hologrampattern for transmitting the first and second laser light withoutdiffracting the first and second laser light while diffracting the thirdlaser light into high-order diffracted light having the order of primaryor higher; an objective lens having the numerical aperture correspondingto the thickness of the first protective layer, the objective lensconverging the first laser light having passed through the first areaincluding the second area onto an information surface on one side of thefirst protective layer, the objective lens converging the second laserlight having passed through the second area onto an information surfaceon one side of the second protective layer, the objective lensconverging the high-order diffracted light having passed through thethird area onto an information surface on one side of the thirdprotective layer; and a holder that holds the polarizing hologramelement, the nonpolarizing hologram element, and the objective lens. 10.The laser converging apparatus according to claim 9, wherein the thirdlaser light is polarized linearly in the first direction, and wherein asectional shape of the nonpolarizing hologram pattern in the directionof the optical axis of the first and second laser light is rectangleswhose depth in a direction of optical axis is integer times acalculation given by dividing the wavelength of the first and secondlaser light by a value given by subtracting 1 from the refractive indexof the nonpolarizing hologram element, or which sectional shape is aserration having stepped slopes whose each depth in the direction of theoptical axis is integer times a calculation given by dividing thewavelength of the first and second laser light by a value given bysubtracting 1 from the refractive index of the nonpolarizing hologramelement.
 11. The laser converging apparatus according to claim 9,wherein the polarizing hologram element has a diffusion hologram patternin a part of the first area other than the second area, the diffusionhologram pattern transmitting the first and third laser light withoutdiffracting the first and third laser light and diffracting the secondlaser light so that the second laser light having passed through thepart of the first area other than the second area is not converged ontothe information surface on one side of the second protective layer. 12.An optical pickup device comprising: (1) a first semiconductor laserthat emits a first laser light linearly polarized in a first direction;(2) a polarizing direction switching element that transmits the firstlaser light while maintaining a polarizing direction of the first laserlight or that transmits a second laser light created by turning thepolarizing direction of the first laser light to a second directioncrossing the first direction; (3) a second semiconductor laser thatemits third laser light having a wavelength different from that of thefirst and second laser light; and (4) a laser converging assemblyincluding: a polarizing hologram element having a first area defined bya numerical aperture corresponding to a thickness of a first protectivelayer of a first disk medium and a second area inside the first area,the second area defined by a numerical aperture corresponding to athickness of a second protective layer (>the thickness of the firstprotective layer) of a second disk medium, the second area having apolarizing hologram pattern for transmitting the first laser lightwithout diffracting the first laser light, diffracting and transmittingthe second laser light, and transmitting the third laser light withoutdiffracting the third laser light; a wavelength selecting nonpolarizinghologram element having a third area defined by a numerical aperturecorresponding to a thickness of a third protective layer (>the thicknessof the first protective layer) of a third disk medium, the third areahaving a nonpolarizing hologram pattern for transmitting the first andsecond laser light without diffracting the first and second laser lightwhile diffracting the third laser light into high-order diffracted lighthaving the order of primary or higher; an objective lens having thenumerical aperture corresponding to the thickness of the firstprotective layer, the objective lens converging the first laser lighthaving passed through the first area including the second area onto aninformation surface on one side of the first protective layer, theobjective lens converging the second laser light having passed throughthe second area onto an information surface on one side of the secondprotective layer, the objective lens converging the high-orderdiffracted light having passed through the third area onto aninformation surface on one side of the third protective layer; and aholder that holds the polarizing hologram element, the nonpolarizinghologram element and the objective lens.
 13. A laser convergingapparatus comprising: a wavelength selecting first nonpolarizinghologram element having a first area defined by a numerical aperturecorresponding to a thickness of a first protective layer of a first diskmedium and a second area inside the first area, the second area definedby a numerical aperture corresponding to a thickness of a secondprotective layer (>the thickness of the first protective layer) of asecond disk medium, the second area having a first hologram pattern fordiffracting first laser light into zero order light and first high-orderdiffracted light having the order of primary or higher whiletransmitting second laser light having a wavelength different from thatof the first laser light without diffracting the second laser light; awavelength selecting second nonpolarizing hologram element having athird area defined by a numerical aperture corresponding to a thicknessof a third protective layer (>the thickness of the first protectivelayer) of a third disk medium, the third area having a second hologrampattern for transmitting the first laser light without diffracting thefirst laser light while diffracting the second laser light into secondhigh-order diffracted light having the order of primary or higher; anobjective lens having the numerical aperture corresponding to thethickness of the first protective layer, the objective lens convergingthe first laser light having passed through a part of the first areaother than the second area and zero order light having passed throughthe second area onto an information surface on one side of the firstprotective layer, the objective lens converging first high-orderdiffracted light having passed through the second area onto aninformation surface on one side of the second protective layer, theobjecting lens converging the second high-order diffracted light havingpassed through the third area onto an information surface on one side ofthe third protective layer; and a holder that holds the firstnonpolarizing hologram element, the second nonpolarizing hologramelement, and the objective lens.
 14. The laser converging apparatusaccording to claim 13, wherein a sectional shape of the first hologrampattern in a direction of optical axis of the second laser light isrectangles whose depth in the direction of the optical axis is integertimes a calculation given by dividing the wavelength of the second laserlight by a value given by subtracting 1 from the refractive index of thefirst nonpolarizing hologram element, or which sectional shape is aserration having stepped slopes whose each depth in the direction of theoptical axis is integer times a calculation given by dividing thewavelength of the second laser light by a value given by subtracting 1from the refractive index of the first nonpolarizing hologram element,and wherein a sectional shape of the second hologram pattern in adirection of optical axis of the first laser light is rectangles whosedepth in the direction of the optical axis is integer times acalculation given by dividing the wavelength of the first laser light bya value given by subtracting 1 from the refractive index of the secondnonpolarizing hologram element, or which sectional shape is a serrationhaving stepped slopes whose each depth in the direction of the opticalaxis is integer times a calculation given by dividing the wavelength ofthe first laser light by a value given by subtracting 1 from therefractive index of the second nonpolarizing hologram element.
 15. Thelaser converging apparatus according to claim 13, wherein the firstnonpolarizing hologram element has a diffusion hologram pattern in apart of the first area other than the second area, the diffusionhologram pattern diffracting the first laser light having passed througha part of the first area other than the second area into zero orderlight and high-order diffracted light having the order of primary orhigher so that the first laser light is not converged onto theinformation surface on one side of the second protective layer.
 16. Anoptical pickup device comprising: (1) a first semiconductor laser thatemits first laser light; (2) a second semiconductor laser that emitssecond laser light having a wavelength different from that of the firstlaser light; and (3) a laser converging assembly including: a wavelengthselecting first nonpolarizing hologram element having a first areadefined by a numerical aperture corresponding to a thickness of a firstprotective layer of a first disk medium and a second area inside thefirst area, the second area defined by a numerical aperturecorresponding to a thickness of a second protective layer (>thethickness of the first protective layer) of a second disk medium, thesecond area having a first hologram pattern for diffracting the firstlaser light into zero order light and first high-order diffracted lighthaving the order of primary or higher while transmitting the secondlaser light without diffracting the second laser light; a wavelengthselecting second nonpolarizing hologram element having a third areadefined by a numerical aperture corresponding to a thickness of a thirdprotective layer (>the thickness of the first protective layer) of athird disk medium, the third area having a second hologram pattern fortransmitting the first laser light without diffracting the first laserlight while diffracting the second laser light into second high-orderdiffracted light having the order of primary or higher; an objectivelens having the numerical aperture corresponding to the thickness of thefirst protective layer, the objective lens converging the first laserlight having passed through a part of the first area other than thesecond area and zero order light having passed through the second areaonto an information surface on one side of the first protective layer,the objecting lens converging first high-order diffracted light havingpassed through the second area onto an information surface on one sideof the second protective layer, the objective lens converging secondhigh-order diffracted light having passed through the third area onto aninformation surface on one side of the third protective layer; and aholder that holds the first nonpolarizing hologram element, the secondnonpolarizing hologram element, and the objective lens.
 17. The opticalpickup device according to claim 4, wherein the polarizing directionswitching element is a liquid crystal element.
 18. The optical pickupdevice according to claim 12, wherein the polarizing direction switchingelement is a liquid crystal element.
 19. An optical diskrecording/reproducing apparatus mounted with the optical pickup deviceaccording to claim
 3. 20. An optical disk recording/reproducingapparatus mounted with the optical pickup device according to claim 8.21. An optical disk recording/reproducing apparatus mounted with theoptical pickup device according to claim
 12. 22. An optical diskrecording/reproducing apparatus mounted with the optical pickup deviceaccording to claim 16.